iFanboy has a distinctly different take on this in their article The Myth of the Sell Out Announcement. I'm not knowledgeable enough about the industry to say if they're right or wrong, but the sales figures cited are so small that even a small underestimate ends up in a "sell out" without the book actually being a hit.

That said, it's a damned shame that something the quality of Nonplayer sold less than 9,000 copies, sell-out or not.